1. Field of the Invention
This invention relates to a battery charging system for charging a battery pack connected to an information processing apparatus, and in particular to a Smart Battery system that reduces power consumed for charging when the information processing apparatus is powered off.
2. Description of Related Art
Portable information processing apparatuses such as notebook computers, which are made advantageously compact, are commonly carried outside the office and used on a train, in a car, or the like. For this reason, notebook computers usually have a charge type battery integrated therein, and may also have a battery provided externally so that the system can be used for a longer period.
At present, intelligent type batteries such as Smart Batteries have been developed. The Smart Battery, which is a charge type battery, includes a microprocessor. By programming the microprocessor, the Smart Battery can transmit information concerning a remaining capacity, a voltage, manufactured date or the like of the battery and different kinds of signals.
FIG. 3 shows a circuit structure of a Smart Battery system including two battery packs, which is supported in a conventional notebook computer. In FIG. 3, there are shown: a Smart Charger 3 for supplying power to charge the Smart Battery packs (hereinafter merely referred to as "battery", or "batteries") 1, 2; a Smart Selector 4 for switchably connecting the Smart Charger to either of the batteries 1 and 2; a host controller 5 for executing a switching control for the Smart Selector 4 to switch the batteries to be connected; and a separate regulator circuit 6 for supplying power from an AC supply or the batteries 1, 2 to the host controller 5. In FIG. 3, a section enclosed by a dashed line (including a CPU etc. 7 and a DC/DC converter 8) contains elements of the circuit in the information processing apparatus that are not relevant to the battery charge. The Smart Selector 4 is connected to each of the elements required for charging, namely the batteries 1, 2, the Smart Charger 3, and the host controller 5, via the System Management Bus (SMBus (Trademark)) provided by Intel. Co., and is controlled through an SMBus interface. The aforementioned data including information concerning the remaining capacity of the battery or the like is transmitted or received via the SMBus. Further, the Smart Selector 4 includes a mechanism for detecting whether or not the batteries 1 and 2 are connected to the Smart Selector 4, and operates such that the Smart Charger 3 is connected to the battery whose connection state is detected to perform charging. In this case, when only one of the two batteries is connected (to the Smart Selector 4), the Smart Selector 4 can operate so that the connected battery is to be charged. However, when both batteries are connected simultaneously, the Smart Selector 4 must select any one of the batteries 1, 2 in accordance with an instruction from the host controller 5 and establish connection between the selected battery and the Smart Charger 3. For example, assume that the battery 1 is integrally mounted in the computer and the battery 2 is externally provided to the computer. In the Smart Battery system, the integrated battery 1 is usually first charged and then charging of the external battery 2 begins after the charging of battery 1 is completed.
Next, the operation at the time of charging the batteries 1 and 2 in the aforementioned structure will be described.
First, when the notebook computer is powered on (system on), the host controller 5 operates using power supplied via the DC/DC converter 8 which constitutes means for controlling a power supply to the computer body, and executes switching control of the Smart Selector 4 while checking the remaining capacity of the batteries 1 and 2.
When the notebook computer is switched off (system off), on the other hand, a power from the AC supply is not supplied to the computer body including the DC/DC converter 8 or the like, and therefore a power from the batteries 1 and 2, not from the DC/DC converter 8, is supplied to the host controller 5 and charging is performed as follows. First, under the control of the host controller 5, the Smart Selector 4 operates to connect the Smart Charger 3 to the integrated battery 1 of the two batteries 1 and 2 which are both in the connected state, thereby supplying power to the battery 1. The battery 1, when reaching a full-charged state, transmits a full charge signal indicating this state. The Smart Selector 4, which, by itself, is not able to switch the objects to which a power is supplied, executes such a switching operation for supplying a power under the control of the host controller 5. Accordingly, the full charge signal from the battery 1 is sent via the Smart Selector 4 to the host controller 5. The host controller 5, when detecting the full charge signal, issues a command to switch the objects to be connected with the Smart Charger 3 to the Smart Selector 4. Then, in response to the command from the host controller 5, the Smart Selector 4 switches the objects to be connected with the Smart Charger 3 into the battery 2 which is another battery whose connected state has been detected. In this way, charging of the battery 2 connected to the Smart Charger 3 will begin.
As described above, in the conventional Smart Battery system, a plurality of batteries 1, 2 are connected to the Smart Selector 4, and the host controller 5, when detecting a full charge signal issued by the battery reaching its full-charged state, executes switching control of the Smart Selector 4, thereby automatically switching the batteries to be charged.
However, in the foregoing conventional system, even when the system is off, power must continuously be supplied to the host controller, which, when detecting the full charge signal issued by the battery, executes a switching control of the Smart Selector which is not able to switch the connecting objects by itself.
Therefore, there are times when the battery capacity becomes inadequate, even though the computer has not been used for a long time after the completion of charge.